Single-loop octane enrichment

ABSTRACT

The present invention provides apparatuses and processes for producing high octane fuel from synthesis gas. The process combines transalkylation and zeolite-forming/aromatization in conjunction with a single recycle loop configuration in order to effectively promote the fuel quality, particularly octane rating. The process involves adding a step for enriching octane of the fuel coming from the single recycle loop process. Preferably, the enrichment step takes place in an octane enrichment reactor containing two different catalysts, a zeolite-forming/aromatization catalyst followed by a transalkylation catalyst. The final fuel product preferably has an octane of about 92 to about 112.

CROSS-REFERENCE TO RELATED APPLICATIONS AND CLAIM TO PRIORITY

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/293,410, filed Feb. 10, 2016, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to apparatuses and processes for producinghigh octane fuel, particularly from US medium octane gas produced fromsynthesis gas.

BACKGROUND

When hydrocarbon stream passes through an acidic zeolite catalyst, twotypical chemical reactions occur. First, the paraffinic and i-paraffinicportions of the stream crack down to form light olefins. Second, thenaphthenic portion is dehydrogenated to form cyclic or chain olefins.Some of these olefins may combine and rearrange to form aromatics, suchas toluene and xylenes. Such aromatic growth is different from thearomatic alkylation pathway in typical methanol-to-gasoline (MTG) wherehighly methyl-substituted benzenes are normally the preferred products.It is known that toluene and xylenes are desirable for high octane,while durene (1,2,4,5-tetramethyl benzene) is not. The generation ofadditional desirable species, such as toluene and xylenes, is always apositive direction for octane enrichment. Besides, naphthenic componentsare known to be undesirable for high octane rating. In addition,iso-durenes are known to be bad actors for viscometric properties, asthey increase the fuel viscosity. The conversion of undesirablenaphthenes into desirable species, such as toluene and xylenes, is oneof the most effective way to enhance octane and improve viscometricproperties of fuel made from synthesis gas (synfuel). Besidesaromatization, the acid zeolite catalyst has the capability fortransalkylation, where methyl groups may be interchanged among aromaticmoieties intra- or inter-molecularly. The zeolite-forming pathway issummarized in FIG. 1.

Zeolite-forming has been extensively studied by Zeosit and exercised inmany refineries, located mostly in Eastern Europe and Russia. Theeconomic evaluation has also been conducted in a comparison to otherreforming technologies based on precious metals (Stepanov et al.,Chemistry for Sustainable Development 13:505-518 (2005); Rovenskaja etal., Chem. Ind. 57(9):399-403 (2003); Erofeev et al., XVIIIInternational Scientific Symposium in Honor of Academician M.A.UsovPGON2014). In contrast to Pt-reforming, zeolite-forming does not requirethe expensive catalysts and the hydrofining stages to remove sulfur andnitrogen species from the raw materials. The regeneration of Pt-basedcatalyst is difficult and not cost effective. Due to the light gas loss,zeolite-forming needs to be optimized between the recovery andefficiency in octane boosting. In other words, the use ofzeolite-forming alone may not be a sufficient way to improve octanerating in synfuel.

Therefore there is a need to increase octane rating in synfuel withoutthe drawbacks discussed above.

SUMMARY OF THE INVENTION

One aspect of the present invention provides a process which combinestransalkylation, zeolite-forming, and aromatization(methanol-to-aromatics) in conjunction with a single recycle loopconfiguration in order to effectively promote the fuel quality,particularly octane rating. The process involves adding a step forenriching octane of the fuel coming from the single recycle loopprocess. Preferably, the enrichment step takes place in an octaneenrichment reactor containing two different catalysts, azeolite-forming/aromatization catalyst followed by a transalkylationcatalyst. The final fuel product preferably has an octane of about 92 toabout 112, more preferably about 95 to about 105, most preferably about98 to about 101.

Another aspect of the present invention provides a process to producehigh octane fuel. The process entails four sequential catalytic stageswith intermediate heat exchange to provide the requisite temperature ineach stage, but with no interstage separation. The unreacted gases fromthe fourth stage are recycled to the first stage after separation of themedium RON (research octane number) fuel from the unreacted gases in acondenser. The medium RON fuel is then lead to the octane enrichmentreactor to increase the octane of the intermediate fuel.

The four sequential catalytic stages are detailed in U.S. Pat. No.8,686,206 ('206 patent), which is incorporated herein by reference. Thefour reactor stages are connected in series, preferably interconnectedwith heat exchangers to adjust the temperature of the outflow of onestage to correspond to the desired inlet temperature of the next stage.Each stage may have one or more reactors in series or in parallel,loaded with the same catalyst. No separation or removal of intermediateproduct is made between the first to fourth stages. The first stageconverts synthesis gas to methanol and water; the second stage convertsa portion of the methanol to dimethylether; the third stage convertsmethanol and dimethylether to fuel products and heavy gasoline; and thefourth stage converts the heavy gasoline via hydrotreating reactions toadditional fuel products.

A further aspect of the present invention provides another process toproduce high octane fuel. The process entails three sequential catalyticstages with intermediate heat exchange to provide the requisitetemperature in each stage, but with no interstage separation. Theunreacted gases from the third stage are recycled to the first stageafter separation of medium RON fuel from the unreacted gases in acondenser. The intermediate fuel is then lead to the octane enrichmentreactor to increase the octane of the intermediate fuel.

The three sequential catalytic stages are detailed in U.S. patentapplication Ser. No. 14/566,233 ('233 application), filed Dec. 10, 2014,which is incorporated herein by reference. The process contains threereactor stages in series, preferably interconnected with heat exchangersto adjust the temperature of the outflow of one stage to correspond tothe desired inlet temperature of the next stage. Each stage may have oneor more reactors in series or in parallel, loaded with the samecatalyst. There is no separation or removal of intermediate product. Forgasoline synthesis, the first stage converts synthesis gas to methanoland water; the second stage converts a portion of the methanol todimethylether; the third stage converts methanol and dimethylether tofuel products and heavy gasoline, and part of the third stage alsoconverts the heavy gasoline components via hydrotreating andtransalkylation reactions to fuel products.

Other aspects of the invention, including apparatus, devices, processes,and the like which constitute part of the invention, will become moreapparent upon reading the following detailed description of theexemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing background and summary, as well as the following detaileddescription of the drawings, will be better understood when read inconjunction with the appended drawings. For the purpose of illustratingthe invention, there is shown in the drawings embodiments which arepresently preferred. It should be understood, however, that theinvention is not limited to the precise arrangements andinstrumentalities shown. In the drawings:

FIG. 1 is a chart showing the zeolite-forming pathways;

FIG. 2 is a schematic showing R5 of the present invention;

FIG. 3 are graphs showing A) octane enhancement (ΔRON); and B) thecorresponding recovery % of the pilot test using catalysts withdifferent ratios of SAR;

FIG. 4 are graphs showing zeolite-forming lifetime evaluation usingtwo-layer configuration in pilot reactor: A) ΔRON as a function of timeon stream; and B) % recovery as a function of time on stream;

FIG. 5 is a graph showing the dependence of aromatics on H₂concentration;

FIG. 6 are graphs showing transalkylation of the reference solution(12.1% wt durene and 87.9% wt toluene) as a function of time on stream(TOS): A) toluene (T), benzene (B), and xylene; B) durene and trimethylbenzenes; and

FIG. 7 is a graph showing the use of the decay rate of durene as anindicator for catalyst degradation.

DETAILED DESCRIPTION

The invention relates to systems and processes for improving octane forfuel produced from synthesis gas (syngas). The final fuel product has anoctane rating of greater than about 92, preferably about 92 to about112, more preferably about 95 to about 105, most preferably about 98 toabout 101. As used herein “high RON fuel” or “high octane fuel” or thelike refers to fuels having RON of greater than 92. In addition, thefinal fuel product has reasonable heat of combustion (greater than about43 MJ/Kg) and a freezing point of less than −58° C.; and contains nolead, no multi-ring compound (only single ring compounds are present),less than about 15 ppm sulfur, and/or less than about 5 ppm nitrogenspecies.

The system of the present invention provides a reactor system to producehigh octane fuel from syngas. Fuel having medium research octane number(RON) (medium RON fuel) may be produced from the four reactors of thesystem (R1 to R4) as provided by U.S. Pat. No. 8,686,206 ('206 patent),which is incorporated herein by reference. The '206 patent provides afour-stage reactor (from R1 to R4) in a single recycle loopconfiguration to provide gasoline synthesis from synthesis gas (syngas)directly in a continuous fashion. That process involved four sequentialcatalytic stages, preferably with intermediate heat exchange, to providethe requisite temperature in each stage, but with no interstageseparation (the process is also referred to herein as the “MTGHprocess”). The first reactor (R1) converts synthesis gas to principallymethanol and some water. The product from the first reactor (R1), avapor mixture of essentially methanol, water and unreacted synthesisgas, flows to a second reactor (R2). The second reactor (R2) converts aportion of the methanol to dimethylether. The product from R2, whichessentially contains methanol, dimethylether, water and unreactedsynthesis gas, flows via a conduit to a third reactor (R3). The thirdreactor (R3) converts methanol and dimethylether to fuel product(gasoline, jet fuel and/or diesel) and heavy gasoline. The product fromR3 contains essentially fuel product (C₅-C₈ hydrocarbons, toluene, andxylene), heavy gasoline (>C8 aromatics) and water, with minor amounts ofunreacted methanol and dimethylether and unreacted synthesis gas. Thisproduct flows to a fourth reactor (R4) to convert the heavy gasoline toa product containing the fuel composition with low heavy gasolinecontent, water, minor amounts of unreacted methanol and dimethyletherand unreacted synthesis gas. This fuel composition can then be separatedfrom the water, the light gases (including light paraffins ≤C4), andunreacted syngas using a separator 202, as shown in FIG. 2. The productfrom R4 may be led to the separator 202 via conduit 200. Othervariations and specific embodiments of the MTGH process disclosed in the'206 patent are appropriate for the present invention. The fuelcomposition produced from the separator 202 may typically have an octanerating of about 84 to about 90, which is the same as the fuel producedin R4 (not including water and unreacted syngas). Fuel containing thisoctane rating is referred to herein as “medium RON fuel” or “mediumoctane fuel” or the like.

Alternatively, the medium RON fuel may be produced by the processdisclosed in co-pending U.S. patent application Ser. No. 14/566,233('233 application), filed Dec. 10, 2014, which is incorporated herein byreference. This process contains three reactors, the first two reactorsare identical to R1 and R2 of the MTGH process disclosed in the '206patent (hence the first two reactors for this process is also referredto herein as R1 and R2). The third reactor (referred to herein as R3/4)is essentially combines R3 and R4 of the MGTH process into a singlestage with the catalysts of R3 and R4 in the same reactor (R3/4). R3/4converts methanol and DME to fuel product (C₅ to C₈ hydrobarbons,toluene, and xylene) and heavy gasoline (>C₈ aromatics), whileconcurrently and synergistically hydrotreating any non-preferredhydrocarbon products. The hydrotreatment reduces the heavy gasoline(trimethylbenzenes and tetramethylbenzenes) to produce the medium RONfuel, such as toluene, xylenes and C₅ to C₈ hydrobarbons, principally C₅to C₇ hydrocarbons. R3/4 carries out both the hydrocarbon synthesis andhydrotreatment reactions in a single reactor. As such, R3/4 contains twodifferent catalysts, one for hydrocarbon synthesis (converts methanoland dimethylether to fuel product (gasoline, jet fuel and/or diesel) andheavy gasoline) and one for hydrotreating the heavy gasoline to mediumRON fuel product. Like the MGTH process, preferably intermediate heatexchangers are provided between the three reactors (R1, R2, and R3/4) toprovide the requisite temperature in each stage, but no interstageseparation is provided. As noted above for the product of R4, theproduct produced by R3/4 may also be led to the separator 202 toseparate the fuel (medium RON) from the water, the light gases(including light paraffins ≤C₄), and unreacted syngas using a separator202, as shown in FIG. 2. Other variations and specific embodiments ofthe process disclosed in the '233 application are appropriate for thepresent invention. Both the processes of the '206 patent and the '233application, may produce medium RON fuel.

The catalysts used in the R1 and R2 are well known in the art from priorMTG processes. Appropriate catalysts for R-1 include, but are notlimited to, CuO/ZnO/Al₂O₃, Zn—Cr and other bifunctional catalysts dopedwith certain elements can also carry methanol synthesis. Appropriatecatalysts for R-2 in gasoline application include, but are not limitedto, gamma-alumina, zeolites and other mesoporous materials can alsocarry methanol dehydration into dimethylether.

The catalyst used in R3 is a hydrocarbon synthesis catalyst thatconverts methanol and dimethylether to fuel product (gasoline and/or jetfuel) and heavy gasoline). Hydrocarbon synthesis catalysts arewell-known in the art from prior MTG processes. Appropriate catalystsfor R-3 include, but are not limited to ZSM-5, SAPO-34 and other MFIzeolites can also carry hydrocarbon synthesis.

The hydrotreating catalysts used in R4 include, but not limited to,certain larger pore zeolites and Group IX or X metal oxide (e.g. nickeloxide) catalyst on alumina reduced in the presence of hydrogen andcarbon monoxide in the absence of sulfur. In certain embodiments, thecatalyst can be Group IX or X metal oxide (e.g. cobalt oxide) catalystcombined with a Group VI metal oxide (molybdenum oxide) catalyst onalumina reduced in the presence of hydrogen and carbon monoxide and inthe absence of sulfur. A specific example of the catalyst includeunsulfided cobalt molybdate on alumina or atomic nickel on alumina, thereduction, if any, being carried out in the presence of synthesis gas.Sulfiding the catalyst surface is not necessary but catalytic reductionusing either a H₂ flow or a mixture of H₂ and CO under operatingtemperature is desirable. Temperature of the fourth stage ranges from120 to 230° C. (248 to 446° F.) depending on the catalyst used, with thepreferred temperature being about 150-180° C. (302 to 356° F.). Thesetemperatures are surprisingly lower than 232 to 427° C. (450 to 800° F.)disclosed by Garwood (U.S. Pat. No. 4,304,951) for treating a 200-400°F. bottoms fraction. We ascribe this valuable difference in temperatureand the more desirable product mix to treating the whole product fromthe fuel forming step in the presence of synthesis gas instead of abottoms fraction with principally hydrogen. We also ascribe thissurprising result to using unsulfided catalysts, unlike Garwood thatteaches by example that mixed oxide catalysts need to be sulfided. Hanet al. (U.S. Pat. No. 4,973,784) teaches the use of zeolites fortreating the durene containing product in the presence of substantialpartial pressure of hydrogen producing undesirable benzene. Our novelprocess does not produce benzene. Still in another variation, Chester etal. (U.S. Pat. No. 4,387,261) propose treating the entire product fromthe fuel forming stage, but preferably a heavy fraction thereof, usingZSM-12, preferably impregnated with platinum, an expensive metal, atelevated temperatures and pressures to dealkylate durene to form xylene,toluene, benzene and undesirable light gases such as C₂ and C₃hydrocarbon. The present process is clearly superior in that it does notproduce light gases in the treating stage (stage 4). Still in anotherexample, Dwyer et al. (U.S. Pat. No. 4,347,397), showed that treatingthe whole or bottoms product from the fuel producing stage with zeolitesprincipally isomerizes the durene to other tetramethylbenzenes, thereby,producing less desirable heavy product than the present process. Thepreferred transalkylation catalyst is Y-zeolite (e.g. USY),beta-zeolite, or combinations thereof. Particularly preferred Y-zeolitesare those with silica to alumina ratios (SAR) of about 10 to about 40.

R3/4 contains two different catalysts, one for hydrocarbon synthesis(used in R3) and one for hydrotreating the heavy gasoline to fuelproduct (used in R4). Preferably, R3/4 contains ZSM-5 as the hydrocarbonsynthesis catalyst and a zeolite catalyst, preferably Y-zeolite, as thehydrotreating catalyst. The zeolite catalyst is used as a hydrotreatingcatalyst, in that it acts to reduce durene and other heavy gasolinecomponents in the mixture through disproportionation, isomerization, andtransalkylation across benzene molecules. The hydrocarbon synthesisreaction that occurs in R3/4 results in a mixture principally comprisedof fuel product (C4-C8 hydrocarbons, toluene, and xylene), heavygasoline (≥C8 aromatics), water, and unreacted synthesis gas. The heavygasoline and highly substituted aromatics in this mixture react in thepresence of the zeolite-based catalyst, preferably Y-zeolite, in R3/4 toproduce the preferred fuel, such as C4-C8 hydrocarbons, toluene, andxylene. The catalyst bed is preferably a mixture of ZSM-5 and zeolite atlevels that are optimized based on operation parameters such as therecycling rate in the system and the environmental temperature in R3/4.The synergy between the ZSM-5 hydrocarbon synthesis catalyst and thezeolite hydrotreatment catalyst in R3/4 results from the formation ofcertain intermediates generated by the zeolite catalyst that serve asco-feeding components promoting performance cycles of hydrocarbon pools.Thus, the hydrotreatment portion feeds back positively to thehydrocarbon synthesis, improving reaction efficiency.

Referring to FIG. 2, the liquid medium RON fuel coming from thecondenser 202 flows into an octane enrichment reactor (R5) 206,preferably using a liquid pump 210 via conduit 204. R5 206 is locateddownstream from the condenser 202 but upstream of a stabilizer (orsecond condenser) 208, so that the high RON fuel coming from R5 206 canbe condensed again in the stabilizer 208. The high RON fuel may becollected at the bottom of the stabilizer 208 in stream 214. At the topof the stabilizer 208, light flue gas (≤C₄) is vented through stream216. In an embodiment, a portion of the gas from the top of thecondenser 202 (which is rich in H₂ and typically vented through stream212) may be directed into R5 206 as a carrier gas. In that case, thecarrier gas makes up about 5 to about 15 weight %, preferably about 10%,of the total feed into R5 206. The amount of carrier gas used iscalculated to achieve a H₂ concentration in R5 206 of about 20 to about50 molar % (based on the total gas in R5 (fuel and carrier gas)).

R5 206 is a catalytic reactor and contains at least two catalysts: onefor zeolite-forming/aromatization and one for transalkylation.Preferably, both catalysts require similar operation conditions(including space velocity, temperature, and pressure). In an exemplaryembodiment, the two catalysts are configured as two separate layers inR5 206. For example, the two layers are configured as two distinct bedsin R5 206 to provide a zeolite zone and a transalkylation zone.Preferably, the medium RON fuel, from the condenser 202, first contactsthe zeolite-forming/aromatization catalyst, preferably at the top of R5206, before proceeding to the transalkylation catalyst, preferably atthe bottom of R5 206. Alternatively, the catalysts may be mixed togetherin a single bed. R5 206 is preferably operated at a temperature of about350 to about 480° C., preferably about 380 to about 450° C., a pressureof about 5 bar to about 35 bar, preferably about 10-25 bar, and/or aweight hourly space velocity (WHSV) of about 1 to about 5 hr⁻¹,preferably about 2 to about 4 hr⁻¹.

In order to match the operation conditions, in certain embodiments,modification of zeolite-forming/aromatization catalyst may be necessary.Modified zeolite with certain metal doping or impregnation is used asthe top layer catalyst in this reactor. The metal may be, but is notlimited to, alkali and alkali earth metals, such as Mg, Ca, K, etc.;transition metals, such as Zn, La, etc., or combinations thereof. Thereactions shown in FIG. 1 may be conducted in the top layer of R5 wherecertain i-paraffins and naphthenes are effectively converted intoaromatics to increase octane. Test results also show that the octanelowering species, such as iso-hexanes, iso-heptanes and methyl- and/ordi-methyl cyclohexanes, substantially decrease (weight percentage maydrop more than 40%), while octane boosters, such as toluene and xylenes,increase about 3-6 times in weight amounts. Such change leads to asignificant boosting in octane rating. The increase of the researchoctane number (ΔRON) may be in the range of about 10-12. Thezeolite-forming/aromatization catalyst may be, but is not limited to,ZSM-5, ZSM-11, mordenite, chabazite, or combinations thereof, with ZSM-5having an SAR of about 25 to about 120 being the preferred catalyst.

The transalkylation catalyst used in the bottom layer of R5 may be thesame catalyst used in R4 as described above. A zeolite basedtransalkylation catalyst is preferably used in the bottom layer of R5 tofurther inhibit durene formation in order to maintain a good viscometricproperty of the high RON fuel product. A typical example is, e.g., thereaction between xylene and durene where the immediate products aretoluene and trimethylbenzenes. The final high octane product (high RON)may be condensed in a stabilizer 208 to separate high RON fuel fromlight flue gas (C₄).

The present invention provides an extension of the system of the '206patent or the '233 application to produce a continuous process forproducing high RON fuel by coupling a zeolite-forming andtransalkylation reactor (R5) with the MTGH process or the process of the'233 application. Most importantly, the transalkylation function of R4is also included and coupled into R5 in order to continuously improveproduct quality. R5 provides an integrated octane enrichment module forthe process of the '206 patent or the '233 application.

During the octane enrichment, certain light gas is generated and therecovery of the high octane product will never reach 100%. In generalthe recovery value varies from about 50% to 90% of the feed, dependingupon the operation conditions (pressure and temperature) and themodification of the catalyst in R5. However, the decomposed lightspecies within the vent gas from the stabilizer may be directed into theupstream reformer that further reacts with the steam to generate syngasthrough the reforming process.

The major difference between the standard zeolite-forming and theoperation of the present invention may be categorized in the followingfew points: (1) the present invention is a continuously integratedsystem where the vent gas derived from R5 may be fed into reformer as asingle loop which is not performed with other zeolite-forming methods;(2) The use of Y or beta zeolites in the lower layer of R5 is aneffective way in combining transalkylation function with zeolite-formingso that the durene level remains low; (3) due to the recycle in thesingle-loop, the present invention is operated under H₂-rich (preferablyabout 20 to about 50 molar % (based on the total gas in R5 (fuel andcarrier gas)) condition where the hydrogen presence assists thedecomposition of highly alkylated aromatics through hydrocracking (it isknown that the highly alkylated aromatics are precursors for cokeformation which adversely impact the catalyst lifetime), which reducecatalyst degradation; and (4) the use of transition metal or alkaliearth metal doping or impregnation on the zeolite catalysts in R5 allowsfor significantly improvement in aromatic enrichment which dramaticallyimprove the recovery or minimize the loss during zeolite-forming.

Without further description, it is believed that one of ordinary skillin the art can, using the preceding description and the followingillustrative examples, make and utilize the catalyst of the presentinvention and practice the claimed methods. The following examples aregiven to illustrate the present invention. It should be understood thatthe invention is not to be limited to the specific conditions or detailsdescribed in the examples.

Example 1

In this example, three zeolite based catalysts with different aciditywere tested using a pilot reactor. The amount size for the gasolinequantity of the pilot reactor is in the range of about 1 Kg/hr.Basically a relatively low octane fuel (RON=81, density ρ=0.705 g/ml)was injected into the reactor with a feeding rate of 7-10 g/minute. Thesystem pressure of the pilot unit was about 10 bars and the reactortemperature was varied from 350° C. to 420° C. The temperature changewas aimed to select the optimal window for highest recovery and the bestoctane enhancement. After the conversion, the octane increase (ΔRON) andthe composition of the final product were evaluated by a PONA analyzer.Both the ΔRON and the recovery % values are plotted in FIG. 3. Thezeolite acidity is characterized by the silica-to-alumina ratio (SAR).The acidity trend is as follows: catalyst-A (SAR=60)>catalyst-B(SAR=90)>catalyst-C (SAR=120).

As shown in FIG. 3, ΔRON increases with the acidity of the catalyst; themore acidic the catalyst, higher the ΔRON. At T=400° C., the most acidiccatalyst, catalyst-A, generated an octane enhancement of nearly 12octane units which was significantly larger than the 8 for catalyst-Band 2 for catalyst-C. However, the recovery % followed a completelyopposite trend of catalyst-A (60%)<catalyst-B (71%)<catalyst-C (88%).The composition information reveals the chemical pathways for suchoctane increase. Take catalyst-A as an example (Table 1), theiso-paraffinic portion drops more than 55% and the naphthenic part dropsmore than 42%. The aromatic portion, as well as the olefinic portion,increases more than 50% from the original fuel to the final product.Among the aromatics, the amounts of toluene and xylenes (octaneboosters) increase dramatically. Apparently, certain iso-paraffinic andnaphthenic compounds may have been converted into aromatics followingthe route described in the equations of FIG. 1.

TABLE 1 The original The fuel after synfuel zeolite-forming Density(g/ml) 0.715 0.814 i-P (iso-paraffins) 50.7% 21.3% P (paraffins)  5.1% 5.5% A (aromatics) 28.6% 58.1% O (olefins)  1.1%  3.1% N (naphthenes)12.3%   7% RON 81    93.5  

It is apparent that the octane enhancement of synfuel product isinversely proportional to the yield (recovery %); hence, the larger theΔRON, the lower the recovery value. Please note all catalysts used inthe example of FIG. 3 were plain zeolite samples with different SARvalues. When the plain catalyst was modified with transition or alkaliearth metal doping, the potency of recovery may significantly beincreased.

Example 2

In this example, we evaluated the catalyst lifetime. Two zeolite basedcatalysts were layered in pilot reactor to test the concept of R5. Thecatalyst in the top layer performs zeolite-forming/aromatization foroctane enrichment (ZSM-5 type catalyst); and the catalyst in the bottomlayer performs transalkylation to reduce durene formation (USY typecatalyst). Both ΔRON and the recovery % are plotted in FIG. 4 againstthe time on stream. At the initial temperature of 350° C., the ΔRONfollowed an exponentially decaying function from 9.6 to 5.5 after 35hours. As the ΔRON leveled off around 5.8, we raised the temperature ofR5 from 350° C. to 380° C., and ΔRON jumped back to 10. Following theexponential decay for another period of 30 hours or so, the ΔRON leveledagain around 7.5. The temperature is again raised to 400° C., and ΔRONjumped rapidly to 10.5.

If the temperature is continuously raised following such sawtoothpattern from 380° C. to 450° C., the overall operation time can beextended to more than 150 hours before any significant degradation ofthe catalyst is observe. Such extension in operation time providesadditional benefit to the standard zeolite-forming operation.Apparently, the benefit comes from the combination of transalkylationfunction with the zeolite-forming function introducing more variables toadjust the optimum operation conditions. The transalkylation in thebottom part of R5 contributes to octane enrichment. The transalkylationis also a function of operation temperature (the higher the temperature,the more potent in methyl rearrangement). The initial ΔRON values, 9.6at 350° C., 10 at 380° C., and 10.5 at 400° C., seem to increaseslightly with the reactor temperature. The leveling off temperatures,5.8 at 350° C. and 8 at 380° C., also follow an increasing trend. Withthe presence of H₂, the lifetime is expected to become even longer. Aswill be discussed in the next section, the hydrocracking of certain highalkyl-substituted aromatics which are known to be coke precursors playimportant roles in lifetime extension.

Example 3

In our single-loop systems (the '206 patent or the '233 application)with the recycling from the vent gas of condenser to R1, the systempressure is high and the gas stream is rich in H₂. As mentioned above,the hydrogen content is expected to have impact on catalyst lifetime. Inthis example, we evaluated the hydrogen impact on octane enrichment. Todo so, we compared the microreactor performance of a typicalzeolite-forming/aromatization catalyst (20 g with SAR-120) with a feedof low octane fuel (RON=81.5) under different gases, N₂ only, N₂/H₂mixture (50:50), and H₂ only (with the total flow of 2000 sccm). Theoperation condition was 400° C. and system pressure P=62 bars. Theresults are listed in Table 2.

TABLE 2 Original Zeolite- Zeolite - Zeolite - low-RON forming formingforming fuel under N2 under N2/H2 under H2 C3 0.00 1.11 0.63 0.62 C40.02 2.37 2.17 3.26 C5 15.04 2.03 3.47 6.90 C6 26.29 1.59 1.99 3.69 C713.88 0.33 0.26 0.67 Paraffin 5.17 3.53 3.25 3.28 i-Paraffin 55.95 6.317.87 12.94 Olefin 1.69 5.32 4.12 2.69 Naphthene 15.10 4.95 4.73 4.44Aromatic 20.75 69.38 70.46 70.57 C15+/unknown 13.32 10.51 9.58 5.08toluene 0.62 17.33 15.40 12.05 m-xylene 2.44 11.21 10.97 10.91 p-xylene1.07 3.34 3.34 3.38 o-xylene 1.01 4.63 4.56 4.57 1,2,4-TMB* 5.85 5.075.75 7.27 1,3,5-TMB* 0.41 1.70 2.44 3.01 1,2,3-TMB* 0.32 0.93 1.04 1.22durene 2.97 5.06 7.23 8.55 i-durene 3.12 6.84 9.86 11.63 Octane (RON)81.50 96.00 95.80 98.90 *TMB = trimethyl benzene

As shown in Table 2, zeolite-forming improved the content of toluene(from 0.62% to 17.33%, nearly ×28) and xylenes (from 4.52% to 19.18%,nearly ×4). It also slightly increased the content of TMB (from 6.58% to7.7%, ×1.1) and durene (from 6.09% to 11.9%, only ×1.7). The increasedconcentration for light aromatics (octane boosters) were significantlyhigher than the heavy aromatics (octane suppressors). This was thereason that ΔRON is still in the positive trend even at high H₂concentration. The concentrations of various fuel components were quitesensitive to H₂ content. The increase of the paraffinic components(C₅-C₇) may have followed an increasing rate of a certain chemistryinvolving hydride transfer or hydrocracking which may be related to theexcess of H₂. This trend can be seen in Table 2. The H₂ concentrationtrends with aromatics, as shown in FIG. 5, may be related tohydrocracking of certain heavy alkylated aromatics (C12+). As the H₂concentration was increased, both durene and TMBs (trimethylbenzenes)concentrations increased slightly while the toluene decreased. Thexylene concentration was somewhat insensitive to H₂ concentration.

We observed that an exothermic reaction occurs in the reactor when H₂ ispresent. As we shut off the carrier H₂, a sudden drop of reactortemperature by 5-6° C. was measured by the bed thermocouple.Hydrocracking processes can be attributed to such exothermic behavior.The zeolite-forming in R5 may favor the formation of certain heavyalkylated aromatics (C₁₅₊) which could crack down to form lighterspecies including durene and TMBs under H₂ rich condition. This can beseen in Table 2 where the concentration of C₁₅₊/unknown decreased withH₂. These C₁₅₊/unknown species are believed to be coke precursors. Thepresence of H₂ assisted in the reduction these coke precursors. Owing tothe reduction coke precursors by H₂, the H₂ rich condition in the systembrought additional benefit in extending catalyst lifetime. Based on ourpilot operation, we do not need to regenerate zeolite catalyst for morethan seven thousand hours. In other words, the lifetime of our catalystcan significantly be extended.

Example 4

This example verified the effectiveness of transalkylation in R5. Thetransalkylation involved intermolecular/intramolecular methylrearrangement or disproportionation of methyl-substituted aromatics sothat the highly methyl-substituted aromatics, such as durene, can bereduced. The main purpose of transalkylation was to reduce unwanteddurene and i-durene in the synfuel product.

To carry out transalkylation evaluation, a reference solution (12.1%durene in toluene solution) was used. This liquid solution wascontinuously injected (at a rate of 0.7 ml/min or 42 ml/hr) into amicroreactor containing 18 g of s USY catalyst (through a HPLC pump)heated under the proper temperature. The pressure and temperature of themicroreactor were maintained at 5 bars and 350° C., respectively. Anamount of 2000 sccm H₂ as carrier gas was flown to match the conditionfavored the methylation mechanism. The product coming out ofmicroreactor was cooled down by a Peltier chiller; and the condensedliquid was analyzed by PONA for composition variation. The results areshown in FIG. 6.

As shown in FIG. 6, the concentration of toluene (T) dropped rapidlyfrom its original 87.9% wt. to 60% in the first hour and then graduallyincreased towards 70% after 2 hr. (FIG. 6A). The initial drop was due tothe initial high activity of transalkylation of the equation T+D→X+TMB(where X, D, and TMB stand for xylenes, durene, and trimethylbenzenes,respectively), while the later slowly increasing portion can beattributed to the gradual degradation of transalkylation where theactivity degrades with time. The durene (D) concentration also droppedrapidly from its original 12.1% to 0.1% in the first 1.5 hr. and thengradually increased to 0.3% at after 3.75 hr. (FIG. 6B). The decay ofreactivity was a measure of catalyst degradation. The xyleneconcentration followed a rough mirror image to toluene (FIG. 6A), whilethe TMB growth followed a mirror image to durene (FIG. 6B). Certainlevel of benzene (B) can also be seen (FIG. 6A), suggesting thepossibility of the reaction T+T→B+X.

The gradual decrease of the transalkylation activity may be used as anindicator of catalyst reactivity in terms of its durene reductioncapability. As shown in FIG. 7, the drop in durene conversion followed anearly linear function with time. Although both efficacy decreases indurene and toluene may be used to indicate the degradation, thequantification of durene was more reliable, because toluene was inexcess in the reference solution. Besides, the growth of xylene seemedto be more quantitative than the growth of TMBs.

Another way to look at transalkylation was to compare molar ratios amongisomers such as i-durene/durene and p-xylene/o-xylene. The thermalequilibrium values for these ratios were i-durene/durene=1.27 andp-xylene/o-xylene=0.8. When the catalysts were not active, these ratioswould be deviated from their equilibrium values. As the catalystreactivity is increased, the ratios would become closer to theequilibrium values. The ratio values following the reaction timesequence are listed in Table 3. It was interesting to note thetransalkylation capability for xylenes was weaker than that for durene.Up to 2.8 hr., the p-xylene/o-xylene ratio had not yet reachedequilibrium, while the i-durene/durene ration had already reached 1.27after 2 hr. Based on thermal equilibrium, the distribution of xyleneshould follow a trend of [m-xylene]>>[o-xylene]>[p-xylene]. Anydeviation from this trend could reflect an additional intramolecularisomerization chemistry.

TABLE 3 Time (minute) 40 80 120 160 202 225 i-durene/durene 1.00 1.161.26 1.28 1.27 1.27 p-xylene/o-xylene 0.70 0.71 0.72 0.74 0.80 0.82

The percentage change of durene conversion can be derived from the ratechanges of durene following the reaction time, as shown in FIG. 7, andthe decay rate for the USY zeolite catalyst was determined to be−0.611%/hr. This decay rate can be used as an indicator to evaluate thecatalyst degradation behavior for various transalkylation catalysts. Adatabase may be built to cover not only the plain catalysts, but alsothe modification ones with metal doping.

Example 5

Metal doping in zeolite is known to be helpful in themethanol-to-aromatic (MTA) process. Transition metals, including thosein the Lanthanide series, are commonly used to modify the catalystpotency. This example verified the addition of zinc and rutheniumelements to improve zeolite-forming/aromatization capability. In thiscase, 1-3% Zn and trace amount of Ru were added onto a typical ZSM-5catalyst through a typical ion-exchange technique. A fixed amount ofreference fuel with known RON was injected into the microreactorcontaining 10 g of catalyst operated under 370° C. and 10 bars. After afixed reaction time, fuel samples were collected for PONA analysis. BothΔRON and recovery % were compared and listed in Table 4.

TABLE 4 Plain catalyst 1% Zn—Ru/ZSM-5 catalyst LHSV (hr⁻¹)* 2.0 1.351.35 1.35 Temperature 370 370 400 430 (° C.) Pressure (bar) 10 3 3 3 H₂(sccm) 250 0 0 0 N₂ (sccm) 250 600 600 600 Aromatics (%) 61.88 55.8764.65 75.28 p-xylene/xylenes 20.6 21.1 19.2 18.3 (mol %) Recovery % 59.765.42 62.32 62.23 RON 95 95.5 99.9 103.3 *LHSV = liquid hourly spacevelocity

At 370° C., there was no obvious improvement in octane increase. Howeverthe recovery seemed to improve to some extent. The temperature may betoo low for effective zeolite-forming/aromatization. As the reactortemperature was raised, the benefit of metal modification can be clearlyseen, as shown in the right three columns of Table 4. The operationunder 430° C., 3 bar, LHSV=1.35 hr⁻¹ using N₂ as a carrier gas appearedto be a good practice where the ΔRON was high and the recovery % wasreasonable.

Example 6

In this example a relatively large pilot unit was used to test thecombination concept of zeolite-forming/aromatization and transalkylationin R5. The generation rate of gasoline product in this pilot unit was 5gal/hr. The R5 unit was installed after the condenser where the rawgasoline product was collected but before the stabilizer where the lightgas within the raw gasoline product was stripped to improve the vaporpressure (RVP) of the product. The configuration was as depicted in FIG.2.

A medium-octane STGH fuel sample was firstly collected in the fuel tank.The composition of this fuel is shown in Table 5 as “original feed”fuel. The engine octane number (PONA simulated RON) for this originalfuel was 90.1. The original fuel was then fed into the reactor toperform zeolite-forming/aromatization using ZSM-5 catalyst (top zone)followed by transalkylation by USY catalyst (bottom zone). Fourconditions were run: condition-1 (both top and bottom zones are in 420°C.), condition-2 (both top and bottom zones are in 400° C.), condition-3(top zone at 400° C., bottom zone at 420° C.), and condition-4 (top zoneat 400 C, bottom zone at 440 C). Table 5 also shows the composition ofthe fuel resulting of each of the four conditions.

TABLE 5 Original Condi- Condi- Condi- Condi- feed tion-1 tion-2 tion-3tion-4 Temperature 420 400 420 440 (° C.) WHSV 3 3 3 3 Appearance greendark yellow dark dark yellow yellow yellow Density 0.702 0.7779 0.77240.7681 0.758 (g/ml) Paraffins 8.6364 5.8502 6.8566 7.3277 7.7374I-paraffins 55.4037 17.6138 27.2548 28.6104 30.3625 Olefins 0.95340.7666 1.0612 1.1737 1.4778 Naphthenes 4.8059 1.9903 2.3948 2.35872.3458 Aromatics 29.3499 67.254 57.3383 56.2199 54.0079 benzene 0.15013.0633 1.8274 1.6648 1.5513 toluene 2.3634 15.4353 11.1065 10.48389.8283 o-xylene 2.279 5.3292 4.4171 4.3510 4.2403 m-xylene 5.157113.4087 11.0391 10.6866 10.2182 p-xylene 2.1328 3.9112 3.6659 3.69353.7201 TMB 11.283 15.1053 13.7358 13.7236 13.4286 durene 1.4788 1.66292.1299 2.0413 1.9646 i-durene 1.9618 2.227 2.8106 2.7329 2.6763 TotalC15+ 0.3909 3.6446 2.6104 2.2334 2.0141 Unknowns 0.4598 2.8806 2.47842.0709 2.0545 P/A(wt) 2.18 0.35 0.59 0.64 0.71 P/A(molar) 3.12 0.53 0.890.97 1.06 D/i-D 0.75 0.75 0.76 0.75 0.73 Tot-xylenes 9.5689 22.649119.1221 18.7311 18.1786 D + i-D 3.4406 3.8899 4.9405 4.7742 4.6409simulated 90.1 102.3 98.8 100.1 99.8 RON *P = paraffin; **A = aromatic;and ***D = durene

As shown in Table 5, the high octane rating can be partly attributed tothe increase in octane boosters, including toluene and xylenes.Naphthenes, octane suppressors, were substantially reduced. By lookingat the redistribution of aromatics, the heavy alkylated aromatics, suchas durene and i-durene, were still high. These heavy alkylated benzenesare known to be octane suppressors. Coupling of transalkylation tozeolite-forming is expected to further improve the fuel quality byreducing the heavy alkylated aromatics. Regardless, relatively highengine octane numbers had been obtained, from 98 to 102.

Although certain presently preferred embodiments of the invention havebeen specifically described herein, it will be apparent to those skilledin the art to which the invention pertains that variations andmodifications of the various embodiments shown and described herein maybe made without departing from the spirit and scope of the invention.Accordingly, it is intended that the invention be limited only to theextent required by the appended claims and the applicable rules of law.

What is claimed is:
 1. A process for producing a high octane fuelcomprising the step of passing a feed stream containing a medium octanefuel through an octane enrichment reactor containing a zeolite formingcatalyst and a transalkylation catalyst; and maintaining a H₂concentration of about 20 to about 50 molar % in the octane enrichmentreactor, wherein the recovery of the high octane fuel is about 50% toabout 90% of the feed stream.
 2. The process of claim 1, wherein themedium octane fuel is produced by i. passing the synthesis gas toconvert synthesis gas to methanol and water, which produces a first exitthrough a first reactor stream; ii. passing the first exit streamthrough a second reactor to convert methanol to dimethylether, whichproduces a second exit stream; iii. passing the second exit streamthrough a third reactor to convert methanol and dimethylether to fueland heavy gasoline, which produces a third exit stream; iv. passing thethird exit stream through a fourth reactor to convert the heavy gasolineto isoparaffins, naphthenes, and less substituted aromatics, whichproduces a fourth exit stream; v. passing the fourth exit stream througha condenser to separate unreacted synthesis gas from the medium octanefuel; and vi. recycling the unreacted synthesis gas to the firstreactor; wherein no removal or separation of the first, second or thirdexit streams are effected during steps a) to d).
 3. The process of claim1, wherein the medium octane fuel is produced by i. passing thesynthesis gas through a first reactor to convert synthesis gas tomethanol and water, which produces the first exit stream; ii. passingthe first exit stream through a second reactor to convert methanol todimethylether, which produces a second exit stream; iii. passing thesecond exit stream through a third reactor containing a third catalystfor converting methanol and dimethylether to fuel and heavy gasoline,and a fourth catalyst for converting the heavy gasoline to isoparaffins,naphthenes, and less substituted aromatics, which produces a third exitstream; iv. passing the third exit stream through a condenser toseparate unreacted synthesis gas from the medium octane fuel; and v.recycling the unreacted synthesis gas, wherein no removal or separationof the first, second, or third exit streams are effected during steps a)to c).
 4. The process of claim 1, wherein the zeolite forming catalystcontacts the medium octane fuel before the transalkylation catalyst. 5.The process of claim 1, wherein the zeolite forming catalyst forms a toplayer in the octane enrichment reactor and the transalkylation catalystfrom a bottom layer in the octane enrichment reactor.
 6. The process ofclaim 1, where in the zeolite-forming catalyst comprises ZSM-5, ZSM-11,mordenite, chabazite, or combinations thereof.
 7. The process of claim1, wherein the transalkylation catalyst comprises Y-zeolite,beta-zeolite, or a combination thereof.
 8. The process of claim 1,wherein the medium octane fuel passes through a first bed containing thezeolite forming catalyst, followed by a second bed containing thetransalkylation catalyst.
 9. The process of claim 1, wherein the octaneenrichment reactor operates at about 350 to about 480° C. and/or about 5bar to about 35 bar.
 10. The process of claim 1, wherein the WHSV of thefeed stream through the octane enrichment reactor is about 1 to about 5hr⁻¹.
 11. The process of claim 1, wherein the feed stream furthercontains H₂.
 12. The process of claim 1, wherein the zeolite formingcatalyst is doped or impregnated with a transition metal or an alkaliearth metal.